The present invention relates to a method of and apparatus for heating liquids such as water utilizing microwave energy and more particularly to an improved method and apparatus for increasing the energy absorption of the liquid medium.
A search of the prior art directed broadly to the concept of heating fluids with microwave energy failed to uncover any prior art reference which discloses the method and apparatus of the present invention. A number of patents were collected which disclose various systems, devices and processes for heating fluids with microwave energy and are listed hereinafter as follows:
______________________________________ 2,585,970 3,668,358 3,891,817 4,152,567 2,978,562 3,754,111 3,920,945 4,165,455 3,535,482 3,778,578 3,963,892 4,178,494 3,607,667 3,812,315 4,029,927 4,236,056 3,663,783 3,816,689 4,114,011 ______________________________________
Typically, in the prior art microwave water heater apparatus, the water is either stored in a tank or container of a given volume and radiated by microwave energy from a magnetron or the like, such as shown in U.S. Pat. Nos. 3,891,817; 3,920,945; 4,029,927; 4,152,567; and 4,165,455, or is passed through a coiled tube or other tubular configuration upon which microwave energy is directed, such as the devices disclosed in U.S. Pat. Nos. 2,978,562; 3,778,578; 3,812,315; 3,816,689; 4,114,011; and 4,236,056.
The tank-or container-type devices disadvantageously result in uneven heating and wasted energy when, for example, the entire volume of water in the tank is heated to the required temperature and maintained at a high temperature even though only a small volume of water may be needed. The tubular coil-type devices, on the other hand, provide more even heating of the water and less wasted energy because, generally speaking, (1) the residence time of all water passing through the microwave energy field is relatively uniform and (2) large volumes of heated water are not stored indefinitely, but only slightly more water than the volumetric demand is heated.
However, one important disadvantage of the tubular coil-type devices is the loss of heat radiated from the large external surface area of the pipes, tubes and conduits carrying the heated water. Unless the pipes, tubes and conduits are individually insulated, they will radiate a substantial amount of heat into the surrounding microwave cavity resulting in wasted heat energy. Microwave water heater manifolds comprising a plurality of interconnected conduits are also disadvantageously subject to leakage at tubing joints, especially at the high heating rates involved in the microwave heating of water.